1. Field of the Invention
Embodiments of the invention relate to reflecting light, and more particularly, to a reflective plate and method for manufacturing the same and a backlight unit for a liquid crystal display (LCD) device using the same. Although the embodiments of the invention are suitable for a wide scope of applications, it is particularly suitable for maintaining uniformity of temperature across a reflective plate and a method for manufacturing the same, and a backlight unit for an LCD device using the same.
2. Discussion of the Related Art
In general, a liquid crystal display device includes a liquid crystal display module, a driving circuit for driving the liquid crystal display module, and a case for protecting the driving circuit and the liquid crystal display module. The liquid crystal display module has a liquid crystal display panel having a matrix of liquid crystal cells in which liquid crystal is injected into a gap between two bonded glass substrates. Switching devices are positioned in each of the liquid crystal cells for switching signals applied to the liquid crystal cells. The liquid crystal display module also includes a backlight unit for providing light to the back side of the liquid crystal display panel. Optical sheets for scattering and diffusing the light from the backlight unit are positioned between the liquid crystal display panel and the backlight unit.
The liquid crystal display panel, the backlight unit, and the optical sheets of the liquid crystal display module are packaged together to prevent light leakage and to protect these components from an external impact. The glass substrates of the liquid crystal display panel in the liquid crystal display module are susceptible to damage due to an external impact. A top case is used to package the backlight unit and the optical sheets together with the liquid crystal display panel. Further, the top case runs along the edges of the liquid crystal display panel such that the liquid crystal display panel can still be viewed. Accordingly, the top case protects the glass substrates of the liquid crystal display panel in the liquid crystal display module from an external impact.
FIG. 1 is an exploded perspective view of the related art liquid crystal display device. As shown in FIG. 1, the liquid crystal display device 10 includes a liquid crystal display panel 20, and a backlight unit 30 for providing light to the liquid crystal display panel 20. The backlight unit 30 includes a fluorescent lamp 31 for emitting light, a lamp housing 32 surrounding the fluorescent lamp 31 in a U shape, a light plate 33 for distributing light from the fluorescent lamp 31, and a reflective plate 34 for reflecting light into the light plate 33. A protective sheet 35, a first prism 36, a second prism 37 and diffusion sheets 38 are positioned in succession on the light plate 33. A bottom cover 39 for receiving and holding both the liquid crystal display panel 20 and the backlight unit 30.
The backlight unit 30 provides light to a display region A of the liquid crystal display panel 20. The display region A of the liquid crystal display panel 20 has a matrix of liquid crystal cells (not shown) in which liquid crystal (not shown) is injected into a gap between two bonded glass substrates (not shown). The liquid crystal display device 10 also includes a driving circuit 40 for driving the liquid crystal display panel 20.
When the fluorescent lamp 31 at one edge of the light plate 33 emits light, the lamp housing 32 focuses and directs the light toward an edge of the light plate 33. Then, the light from the edge of the light plate spreads throughout the entire surface of the light plate 33 and is redirected toward the display region A of the liquid crystal display panel 30 through the protective sheet 35, the first prism 36, the second prism 37 and the diffusion sheets 38. A thin film transistor on the liquid crystal display panel controls transmission of the light through a pixel in response to a signal from the driving circuit of the liquid crystal display device. Together, the pixels display a picture on the display region of the liquid crystal display panel.
FIG. 2 is a plan view of the related art backlight unit, and FIG. 3 is a cross-sectional view of the related art backlight unit in FIG. 2 along line II-II′. As shown in FIGS. 2 and 3, the related art backlight unit 50 includes a lamp 51 for emitting light, a lamp housing 52 for holding the lamp 51 and reflecting light from the lamp 51 toward one direction, and a light plate 53 for distributing the light from the lamp 51 into a planar light and providing the planar light to a liquid crystal display panel (not shown). The related art backlight unit 50 also includes a reflective plate 54 on a back side of the light plate 53 for reflecting the light toward the liquid crystal display panel, an optical sheet 55 on the light plate 53 for enhancing a luminance of the light, and a cover bottom 56 for supporting an assembly of the lamp housing 52 and the light plate 53. The reflective plate 54 under the light plate 53 re-reflects light directed thereto through a bottom surface of the light plate 53, thereby increasing light utilization efficiency.
The lamp 51 is typically a cold cathode fluorescent lamp, and the light plate 53 has a scattering pattern (not shown) formed at a predetermined portion thereof for scattering light and a reflecting portion (not shown) in which the light is internally reflected. The light plate 53 has a display region (not shown) and a non-display region (not shown). Light entering into the light plate 53 through a light incident surface at an edge of the light plate 53 from the lamp 51 advances toward the display region of the light plate 53 through the non-display region in which the light is internally reflected. The light is scattered by the scattering pattern in the display region.
FIG. 4 is a cross-sectional view of the lamp housing in the related art backlight unit. Referring to FIG. 4, the lamp housing 52 has aluminum (Al) film 52a and a reflective film 52b, such as polypropylene (PP) or Polyethylene Terephthalate (PET), bonded together with an adhesive 52c. The reflective film 52b is placed on an inner side of the lamp housing 52 and the aluminum film 52a is placed on an outer side of the lamp housing 52. More specifically, the reflective film 52b portion is on the inner side of the lamp housing 52 for reflecting the light from the lamp 51 in one direction, and the aluminum film 52a is on the outer side for dissipating heat from the lamp 51 to outside of the liquid crystal display panel. The reflective plate 52 of the related art backlight unit is a reflective film, such as polypropylene (PP) or Polyethylene Terephthalate (PET), coated onto a back side of the light plate 53.
Because the backlight unit has the reflective film on the inside of the lamp housing and on the backside of the light plate, heat from the lamp can not efficiently dissipate to the bottom cover through the lamp housing. In effect, the reflective films act as insulation. Thus, heat builds up within the backlight unit that effects the liquid crystal display panel. Such heat build-up can cause deformation of the components within the liquid crystal display panel. Moreover, deformation of the optical sheet and the large view angle polarization plate of a LCD device causes light leakage at upper and lower corners of the display panel.